In design, and software design is no exception, simplicity is hard. It's not just a matter of reducing the number of variables or applying Occam's Razor, although this may help to a degree. Simplicity does not mean trivialing either. Sometimes particularly, in visual design, simplicity can be knowing about people. A design can be arranged in an intuitive way, the complexity reduced not by removal; but rearranging to appeal to intuition. Some software packages, like word, have more functions than ever--- the number of functions hasn't decreased; some would say that makes them less usable. But on the hole, the functions that most people want from word are readibly available.
People often talk about 80/20 rule: the A high percentage of effects in any large system are caused by a low percentage of the variables. First attributed to the Italian economist Vifredo Pareto, who observed 20 percent of italians had 80 percent of the wealth. It is known as Pareto's Principle.
Presenting a simple design to the user in software may lead to essential complexity.